This invention relates to a flame-retardant polyolefin-type resin composition, to a method for the preparation thereof, and to flame-retardant cables coated with the composition. More particularly, this invention relates to a highly flame-retardant, highly moldable flame-retardant polyolefin-type resin composition that exhibits excellent mechanical strength, to a method for the preparation of same, and to flame-retardant cables having a coating of the aforesaid flame-retardant polyolefin-type resin composition
One method used to impart flame retardancy to polyolefin-type resins, e.g., polyethylene resins and ethylene-vinyl acetate copolymer resins, comprises blending polyolefin-type resin with a halogen-containing compound (chlorine is a typical example of the halogen). However, halogenated compound-loaded polyolefin-type resin compositions of this type, in addition to evolving large amounts of black smoke during burning, produce gases harmful to humans and corrosive to metals. The addition of the powder of a hydrated metal compound, such as aluminum hydroxide powder or magnesium hydroxide powder, to polyolefin-type resin has already been proposed in order to address the problems described above for halogenated compounds. Unfortunately, this approach has required the addition of large amounts of the hydrated metal compound powder in order to impart flame retardancy to the polyolefin-type resin, and this high loading requirement has prevented the production of anything other than flame-retardant polyolefin-type resins with poor moldabilities and diminished mechanical strength. Japanese Laid Open Patent Application Number Hei 5-339510 (339,510/1993) teaches the production of flame-retardant polyolefin-type resin compositions by the addition of alkoxy-functional branched organosiloxane resin, phosphate ester, and metal hydroxide to thermoplastic resins such as styrenic resins and polyolefin-type resins. One problem with this method is that it affords a flame-retardant polyolefin-type resin composition whose flame retardancy is not entirely satisfactory. Moreover, because it requires the use of phosphate ester, this method, for example, may be unacceptable depending on the particular application and, within the context of disposal, because of the concern of soil pollution by phosphorus compounds.
The inventors achieved this invention as a result of intensive investigations directed to solving the problems described above. In specific terms, an object of this invention is to provide a highly moldable and flame-retardant polyolefin-type resin composition. Additional objects of this invention are to provide a method for producing this flame-retardant polyolefin-type resin composition and to provide flame-retardant cables.